Bulk materials are utilized and produced in industrial applications such as cement production, scrap material processing, and process waste handling. Bulk materials can be characterized as materials used in industrial applications that are transported in high volumes on a continuously moving means such as a conveyor belt after the materials are crushed or otherwise reduced in size for purposes of easier handling in downstream production. Bulk materials can further be characterized as raw materials that are combined in proportion and processed to form another material (such as pre-blended materials), the resulting combination of mixed raw materials (such as post-blended materials) in a homogeneous or non-homogeneous form, scrap materials, and process waste. Bulk materials can also be characterized as materials with low unit value (i.e., individual amounts less than one ton in weight have essentially very small commercial values). In order to achieve economical processing, large volumes are transported to the downstream production units where the relatively valuable mineral contents are separated, or the comminution processes reduce the mass to manageable particle sizes for chemical, hydrometallurgical, or pyroprocessing stages. Therefore, no one particle has more or less value than its neighbor (unlike high value particles that undergo separation as with contained precious metals or gemstones from mass materials), and all material is treated “in bulk.” Typical bulk materials include heterogeneous masses of coarsely crushed mined or quarried bulk materials such as ores of limestone, bauxite, copper, zinc, lead, iron, silica, phosphate rock, potash, clay, rare earths. Other bulk materials transported similarly include scrap materials, chalk, coal and coke, alumina, marl, pyrite, fly ash, process waste, etc. Such bulk materials are utilized in process streams in which the bulk materials are fed or supplied from a source continuously, in batches, or over an extended period of time.
In some processes that utilize bulk materials, components or raw materials are transported from dispensing sources (such as bins or silos), mixed together, and processed to form a new material. Typically, bulk materials are transported through these processes in large volumes utilizing conveyor belts. Many processes that transport high volumes of bulk materials also use pneumatic tubes or air slides to transfer the bulk materials between process points.
During the transportation and processing of bulk materials, it becomes necessary to analyze the exact or average chemical or mineral content and composition of the bulk material for control purposes. Such analysis is especially necessary when the bulk materials are mixed, ground, or processed to form new materials. In the context of process waste, the characterization of bulk materials can be effective in diagnosing the effectiveness of a process and monitoring for contaminants. Acquiring sufficiently accurate and detailed knowledge of the physical and chemical state of a moving stream of bulk materials can be difficult and challenging.
Cement processing is characterized by the processing and formation of bulk materials. Cement can be formed by mixing and intergrinding different raw material components in the dry condition (dry process) or it may be done in water (wet process). A flow diagram for a cement manufacturing process is depicted in FIG. 1. In this typical version of the cement manufacturing process, one or more feeders 100-102 introduce 110-112 crushed raw components on to conveyor belts 105-107. The type of raw components combined to ultimately form cement depends on the type of cement being produced and the composition of the raw components being utilized. Typical raw components include calcareous materials (such as limestone, marl, chalk, oyster shells, aragonite and the like), argillaceous materials (such as clay, shale, slate, slag, fly ash, sand, sandstone and the like), ferruginous material (such as mill scale, iron ore or pyrites), alumina (such as bauxite or materials high in alumina) and certain additives that contribute to the characteristics of the cement. In some parts of the world, limestone, marls and the like that include the calcareous component may also include sufficient proportions of the argillaceous material, such as aluminum oxide and iron oxide, so that only siliceous materials need to be added. Siliceous materials can similarly contain argillaceous material so that such siliceous material may incorporate the needed aluminum oxides. Each raw component can have a different mass particle size. For instance, one raw component may have a greater relative particle size while another raw component may have a much smaller average particle size. As a result, the overall admixture of these components can differ in terms of different chemistry as well as widely different particle sizes.
The crushed raw components are typically conveyed to a second conveyor belt 115 and admixed 120 on the conveyor belt 115 in predetermined proportions. The proportions in which the raw components are admixed can be controlled by the rate in which the feeders dispense the raw components and the rate at which the first conveyor belts transport the raw components. As a result, each of the raw components is admixed at different rates of quantity per unit time. Table 1 shows the relative mineral composition of a typical admixture:
TABLE 1Dry BasisCompositionOxideRange* (%)SiO220 (5-25)Al2O38 (0-8)Fe2O38 (0-8)CaO 30 (25-55)MgO6 (0-6)K2O3 (0-3)Na2O3 (0-3)SO33 (0-3)
In dry processing, the admixed raw components are transported through a series of coarse and/or fine grinding mills 125. The mills integrate 135 the raw components into a homogeneous mixture and dispense a coarse granulation, such as between 50 and 100 mesh, or a fine granulation, such as smaller than 100 mesh, respectively. The mills can be any kind of grinding apparatus, such as an industrial roller, rotary mill, ball mill, disc mill, cage mill, muller mill, high speed mill or the like. These mills dispense the resulting raw mixture onto subsequent conveyor belts, pneumatic tubes or air slides 130, which transport the raw mixture to other mills or process stations. Upon completion of the processing of the raw mixture, the raw mixture is conveyed to a kiln 140.
During the transport of the raw components and the raw mixture from the feeders to the kiln other processing steps and apparatuses optionally may be included. These additional steps and apparatuses may be additional crushers, feeders that provide additional additives to the raw mixture, transport belts, storage facilities and the like.
The kiln can be vertically angled and mounted such that it can be rotated about its central longitudinal axis. The raw mixture is introduced at the top (or feed end) of the kiln and transported down the length of the kiln under the force of gravity. The kiln operates at temperatures on the order of 1,000 degrees Celsius. As the raw mixture passes through the kiln, the raw mixture is calcined (reduced, in chemical terms). Water and carbon dioxide are driven off, chemical reactions take place between the components of the raw mixture, and the components of the raw mixture fuse to form what is known as clinker. In the course of these reactions new compounds are formed. The fusion temperature depends on the chemical composition of the feed materials and the type and amount of fluxes that are present in the mixture. The principal fluxes are alumina (Al2O3) and iron oxide (Fe2O3), which enable the chemical reactions to occur at relatively lower temperatures.
The clinker thus formed is discharged 150 typically onto a grate-type cooler. The cooled clinker is then transported by conveyor belt, pneumatic tube or air slide 145, where a feeder 155 dispenses and admixes 160 gypsum to the clinker. The mixture is transported to a mill 165, which crushes the clinker and homogeneously mixes the gypsum into the composition forming a fine powder cement composition. The mill 165 dispenses the cement composition onto a conveyor belt 170, 180, 185 or into a transport tube or air slide, that transports 175 the cement to silos 190,195 for storage.
Wet systems involve processing the raw components through suitable crushers, grinders and mills either individually or as an admixed composition to the desired level of fineness. The raw components are then fed into water to form slurry. The slurry is transported to a storage tank for that purpose and is constantly agitated. At this stage the slurry can be tested and additives can be included. The slurry is then reduced to a desired fineness by feeding the slurry through suitable crushers, grinders and mills. The slurry is eventually fed into the kiln and processed as in the dry process procedure.
One important consideration in the creation of cement is that the proportion of components must be maintained within narrow limits. Differences in the amount of components introduced in the raw mixture and differences in the composition of the components formed during processing affect the quality and grade of cement. Other factors that influence the type of cement produced include temperature, residence time, size of the particles, and intimacy of contact between the particles. As a result, care must be taken in making decisions to consider both upstream conditions and predict downstream results when any adjustments are made to the mix of raw components materials in order to achieve the desired result.
Traditionally, analysis and monitoring of either raw material components, blended materials such as the raw mixture, and processed cement has been accomplished by extracting samples from the continuous flow and transporting them either manually or via an automatic “tube post” pneumatic capsule sampling and conveying system from the sampling point to a central laboratory for analysis. The laboratory would then prepare and analyze the samples utilizing a variety of standard equipment and instruments. The results of these analyses are then used to adjust factors such as the rate at which the raw components are proportioned to achieve a desired blend recipe.
This arrangement, while providing high accuracies, is deficient because the aggregate time required for sampling, splitting, transport, preparation, and analysis can vary from a minimum of 15-30 minutes to an hour or more. During this delay, the stream of components and mixtures continue to be processed such that tons of the fast-moving bulk materials represented by each sample analyzed have long passed points of control and adjustment. The path followed by these materials from the feeders, along the conveyor belts, through the grinders and kiln and into the silos is a continuous flow (or stream). Any adjustments subsequently made to the process will not be able to correct deficiencies in raw mixtures and processed cement that have moved beyond positions in which corrective action may be taken. These adjustments will only affect raw components, raw mixtures and processed cement that are generated subsequent to the adjustments.
Another difficulty with the above is that this method does not provide a solution to potential problems that require prompt dynamic corrective actions. For instance, the rate of admixing raw components depends not only on the type of materials being mixed but also on the composition of those components. If a feeder contains raw components that lack compositional uniformity, the sample analysis may not be representative of the current stream. Thus, any adjustments that are made after a sample analysis may not be appropriate for the current components and respective composition of those components.
For instance, U.S. Pat. No. 4,026,717 describes a method for monitoring the production of cement in which samples are taken from the material flow stream at various points along the process. After the samples are processed by a coarse mill, a pre-kiln sampler using a bucket extracts samples every 15 seconds and deposits the samples on a second conveyor belt. The belt transports the samples to a blending mill that collects develops a composite sample over 15 minute time period. A conveyor then transports the composite sample to an x-ray analyzer. These samplers are also disclosed for extracting samples from the kiln and the clinker cooling system.
Analysis of cement bulk materials can also require knowledge of the oxides or mineralogical phases (molecular polymorphs), or a standard calculated module based on the quantity of the oxides (or other desired measured properties) present, for standard quality control. Some analytical devices used may not measure either oxide or actual phases directly, but only the elemental values.
A few methods to achieve elemental, and thereby, oxide forms of the chemical constituents of the various raw or blended materials have been utilized. They are, however, limited in terms of practical application and mainly make use of atomic events based upon neutron activation via nuclear activation. These so-called Prompt Gamma Neutron Activation Analysis (PGNAA) systems require either radioactive isotopes for neutron flux, such as the isotope of Californium, Cf252, or a neutron generator (tube). In these cases, the introduced neutrons cause momentary and temporary disequilibrium of the nuclei of contained materials resulting in emission of gamma radiation signatures as a reaction to restore equilibrium. Neutron activation systems apply a potentially hazardous (to humans) technique which requires protective permanent careful shielding to avoid and minimize direct or indirect exposure and frequent costly isotope or generator tube replacements. The short half-life of Cf252 at only approximately two and a half years and the requirement for replacement of neutron tube generators, normally every one to one and a half years, represent both expensive maintenance costs as well as the need to address increasing difficulties in convincing authorities of the public safety in transport and operation of both these types of neutron sources. Further, the resultant gamma radiation from the neutron activation of bulk materials that is caused by neutron flux bombardment of the nuclei of the irradiated materials represents potential additional health and environmental hazards. Other on-line techniques that have been attempted, such as high-power X-ray tube systems, or X-ray diffraction systems, may also require strict adherence to local regulatory authorities. In some venues, the presence of certain of these various classes of all of such devices may be restricted or prohibited altogether.
What is desired therefore is a system and method for analyzing bulk materials that provides real-time analyses for rapid and real-time control of the composition of the bulk material. Also desired is such a system and method that does not alter or touch (either physically or chemically) the streaming bulk materials.